In an internal combustion engine, the “ignition system” is the mechanism that ignites the fuel consumed by the engine. Most engines use either an electrical or a compression heating ignition system. Electrical spark ignition systems rely on a battery and an induction coil to provide an electrical spark to ignite the air-fuel mix in the engine's cylinders. Compression heating ignition systems inject fuel into the engine's cylinders and rely on the heat created in the air by compression in the cylinders to ignite the fuel.
Today's engines must meet the demands of government regulations and consumers for low emissions and high fuel economy. One approach to satisfying these demands is the use of a highly dilute pre-mixed fuel for ignition. However, in the case of spark ignition systems, only a limited amount of dilution is tolerable before misfire and unstable operation occur.
To overcome this shortcoming of spark ignition systems, “pilot” ignition systems have been developed. A small quantity of liquid fuel is injected into a pre-combustion chamber to allow high energy self-ignition. Direct injection pilot ignition systems using diesel fuel have proven to increase the dilution tolerance of both stoichiometric and lean burn engines.
In the case of a non-diesel engine, the use of the diesel-fueled pilot ignition system requires two different fuels for engine operation. Both fuels must be available for re-fueling, and for vehicle engines, both fuels must be carried on-board.